U.S. patent number 6,004,425 [Application Number 08/875,825] was granted by the patent office on 1999-12-21 for rubber-based structural white-shell adhesives.
This patent grant is currently assigned to Henkel-Teroson GmbH. Invention is credited to Peter Born, Frank Dittrich.
United States Patent |
6,004,425 |
Born , et al. |
December 21, 1999 |
Rubber-based structural white-shell adhesives
Abstract
One-component hot-curing structural adhesives based on liquid
rubbers, which may optionally contain functional groups, solid
rubbers, thermoplastic polymer powders and sulfur and also
vulcanization accelerators are suitable for bonding metal parts.
Tensile shear strengths of more than 15 MPa and high breaking
elongations of more than 15% can be obtained. These adhesives are
substantially free from low molecular weight epoxy resins and are
particularly suitable for use in white-shell assembly in the car
industry.
Inventors: |
Born; Peter (Sandhausen,
DE), Dittrich; Frank (Sinsheim, DE) |
Assignee: |
Henkel-Teroson GmbH
(Heidelberg, DE)
|
Family
ID: |
7752365 |
Appl.
No.: |
08/875,825 |
Filed: |
July 25, 1997 |
PCT
Filed: |
January 18, 1996 |
PCT No.: |
PCT/EP96/00194 |
371
Date: |
July 25, 1997 |
102(e)
Date: |
July 25, 1997 |
PCT
Pub. No.: |
WO96/23040 |
PCT
Pub. Date: |
August 01, 1996 |
Foreign Application Priority Data
|
|
|
|
|
Jan 26, 1995 [DE] |
|
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195 02 381 |
|
Current U.S.
Class: |
156/333; 156/334;
525/196; 525/193; 524/433; 524/524; 427/385.5; 427/388.2; 524/525;
524/527; 524/523; 524/534; 525/194; 525/222; 525/313; 525/227;
525/235 |
Current CPC
Class: |
C09J
109/00 (20130101); C09J 109/00 (20130101); C08L
2666/06 (20130101); C08L 2666/06 (20130101) |
Current International
Class: |
C09J
109/00 (20060101); C09J 127/06 (); C09J 131/04 ();
C09J 109/00 () |
Field of
Search: |
;525/193,194,196,222,227,235,313 ;156/333,334 ;427/388.2,385.5
;524/523,524,534,433,525,527 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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2 000 569 |
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Apr 1990 |
|
CA |
|
0 097 394 |
|
Jan 1984 |
|
EP |
|
0 309 903 |
|
Apr 1989 |
|
EP |
|
0 441 244 |
|
Aug 1991 |
|
EP |
|
0 524 058 |
|
Jan 1993 |
|
EP |
|
24 54 235 |
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May 1976 |
|
DE |
|
38 34 818 |
|
Nov 1989 |
|
DE |
|
40 27 064 |
|
Apr 1992 |
|
DE |
|
40 34 725 |
|
May 1992 |
|
DE |
|
056597 |
|
May 1975 |
|
JP |
|
044861 |
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Apr 1977 |
|
JP |
|
201384 |
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Aug 1989 |
|
JP |
|
Other References
Int. J. Adhesion and Adhesives 4(4): 148-150 (1984). .
DIN 53504 (1994)..
|
Primary Examiner: Buttner; David
Attorney, Agent or Firm: Szoke; Ernest G. Jaeschke; Wayne C.
Harper; Stephen D.
Claims
What is claimed is:
1. A one-component adhesive composition substantially free of epoxy
resin and consisting essentially of:
(a) at least one liquid rubber having a molecular, weight below
20,000 present in an amount of between 5% and 50% by weight,
(b) at least one thermoplastic polymer powder having an average
particle size below 1 mm present in an amount of between 2% and 20%
by weight, said thermoplastic polymer powder being selected from
the group consisting of vinyl acetate homopolymers, vinyl acetate
copolymers, ethylene/vinyl acetate copolymers, vinyl chloride
homopolymers, vinyl chloride copolymers, styrene homopolymers,
styrene/methacrylic acid copolymer (meth)acrylate homopolymers,
(meth)acrylate copolymers, polyvinyl acetals, and mixtures
thereof,
(c) a vulcanization system for said composition comprised of a
vulcanizing agent selected from the group consisting of elemental
sulfur, thiuram disulfides, organic peroxides, polyfunctional
amines, quinones, p-benzoquinone dioxime, p-nitrosobenzene,
dinitrosobenzene and mixtures thereof,
(d) at least one filler present in an amount of between 10% and 70%
by weight, all weights being based on the weight of said
composition;
said composition being curable at a temperature of between
80.degree. C. and 240.degree. C., and when cured, having a breaking
elongation according to DIN 53504 of more than about 15% and a
tensile shear strength of at least 9.4 mPa and forming a permanent
adhesive bond to a metal surface.
2. The composition as claimed in claim 1, further consisting
essentially of at least one solid rubber in a quantity of about
1.5% by weight to about 9% by weight, based on the composition as a
whole.
3. The composition as claimed in claim 1, further consisting
essentially of at least one solid rubber in a quantity of about 4%
by weight to about 6% by weight, based on the composition as a
whole.
4. The composition as claimed in claim 1, wherein said
vulcanization system is comprised of sulfur, at least one organic
vulcanization accelerator, and at least one zinc compound.
5. The composition as claimed in claim 1, wherein said
vulcanization system comprises about 4% by weight to about 15% by
weight of powder-form sulfur, about 2% by weight to about 8% by
weight of one or more organic accelerators and about 1% by weight
to about 8% by weight of one or more zinc compounds, the
percentages by weight being based on the composition as a
whole.
6. The composition as claimed in claim 5 wherein the powder-form
sulfur comprises about 5% by weight to about 10% by weight of the
composition as a whole.
7. The composition as claimed in claim 5 wherein the organic
accelerators comprise about 3% by weight to about 6% by weight of
the composition as a whole.
8. The composition as claimed in claim 5 wherein the zinc compounds
comprise about 2% by weight to about 6% by weight of the
composition as a whole.
9. The composition as claimed in claim 5, wherein zinc oxide is one
of the zinc compounds.
10. The composition as claimed in claim 1, wherein said
thermoplastic polymer powder has an average particle size below
about 350 microns.
11. The composition as claimed in claim 1, wherein said
thermoplastic polymer powder has an average particle size of
between 20 and 100 microns.
12. The composition as claimed in claim 1, wherein said composition
is substantially free from plasticizers for the thermoplastic
polymer.
13. The composition as claimed in claim 1, further containing an
ingredient selected from the group consisting of rheology, aids,
extender oils, primers, tackifiers, antiagers and mixtures
thereof.
14. A process for the production of the composition claimed in
claim 1, comprising the step of high-shear mixing of the
components.
15. In a process comprising a step of adhering metal components
with a one-component structural adhesive, wherein the improvement
comprises adhering said metal components with the composition of
claim 1.
16. The improved process claimed in claim 15 wherein the process
comprises white-shell assembly in car manufacture.
17. A process for bonding metal parts or for sealing joints between
metal parts, comprising the steps of:
coating at least one surface of an at least one first part with the
composition claimed in claim 1;
fitting together the at least one first part with an at least one
second part to be joined; and
heating the fitted parts to a temperature of between 80.degree. C.
and 240.degree. C., wherein said heating cures said composition and
joins said parts.
18. The process claimed in claim 17 further comprising the step of
mechanically joining the fitted parts before the step of heating
the fitted parts.
19. A process for coating structural components comprising the
steps of:
spraying or extruding the composition claimed in claim 1 onto the
surface of a part; and
heating the coated part to a temperature of between 80.degree. C.
and 240.degree. C., wherein said heating of said part cures the
composition.
20. A process for coating, bonding or sealing structural components
comprising the steps of:
extruding the composition claimed in claim 1 in the form of a film,
cord or tape, applying said extruded composition to at least one
first structural component; and
heating the structural component or components to a temperature of
between 80.degree. C. and 240.degree. C.
21. The process claimed in claim 20 further comprising the step of
fitting together the at least one structural component to at least
one second structural component before said heating.
22. The composition as claimed in claim 1, having a tensile shear
strength of at least 15 mPa.
23. The composition as claimed in claim 1, wherein the liquid
rubber has a molecular weight of from 900 to 10,000.
24. The composition as claimed in claim 1, wherein the liquid
rubber is selected from the group consisting of polybutadienes,
polybutenes, polyisobutylenes, polyisoprenes, styrene/butadiene
copolymers, butadiene/acrylonitrile copolymers, and mixtures
thereof.
25. The composition as claimed in claim 1, wherein the liquid
rubber contains functional groups selected from the group
consisting of hydroxy, amino, carboxyl, carboxylic anhydride, epoxy
and combinations thereof.
26. The composition as claimed in claim 1 containing at least two
liquid rubbers, one liquid rubber having a high percentage of
cis-1,4-double bonds and another liquid rubber having a high
percentage of vinyl double bonds.
27. A one component adhesive composition substantially free of
epoxy resin and consisting essentially of:
(a) at least one liquid rubber having a molecular weight of from
900 to 10,000 present in an amount of between 5% and 50% by weight,
said liquid rubber being selected from the group consisting of
polybutadienes, polybutenes, polyisobutylenes, polyisoprenes,
styrene/butadiene copolymers, butadiene/acrylonitrile copolymers,
and mixtures thereof;
(b) at least one thermoplastic polymer powder having an average
particle size below 350 .mu.m present in an amount of between 10%
and 15% by weight, said thermoplastic polymer powder being selected
from the group consisting of vinyl acetate homopolymers, vinyl
acetate copolymers, ethylene/vinyl acetate copolymers, vinyl
chloride homopolymers, vinyl chloride copolymers, styrene
homopolymers, styrene copolymers, (meth)acrylate homopolymers,
(meth)acrylate copolymers, polyvinyl acetals, and mixtures
thereof;
(c) a vulcanization system comprised of 4% to 15% by weight
elemental sulfur, 2% to 8% by weight of one or more organic
accelerators, and 1% to 10% by weight of one or more zinc
compounds;
(d) at least one filler present in an amount of 25% to 60% by
weight;
(e) at least one stabilizer present in an amount of 0.1% to 5% by
weight;
(f) at least one solid rubber present in an amount of 1.5% to 9% by
weight, all weights being based on the weight of said
composition;
said composition being curable at a temperature of between
160.degree. C. and 200.degree. C., and, when cured, having a
breaking elongation according to DIN 53504 of more than about 20%
and a tensile shear strength of at least 15 mPa and forming a
permanent adhesive bond to a metal surface.
28. The composition as claimed in claim 27, wherein at least one
solid rubber is selected from the group consisting of
polybutadienes, styrene/butadiene rubbers, butadiene/acrylonitrile
rubbers, isoprene rubbers, butyl rubbers, and polyurethane
rubbers.
29. The composition as claimed in claim 27, wherein at least one
solid rubber is a polybutadiene rubber having a percentage of
cis-1,4-double bonds above 95%.
30. The composition as claimed in claim 27, wherein at least one
thermoplastic polymer has an average particle size from 20 .mu.m to
100 .mu.m and is selected from the group consisting of polyvinyl
acetates, ethylene/vinyl acetate copolymers, polyvinyl chlorides,
polymethyl methacrylates, and styrene methacrylates.
31. The composition as claimed in claim 27, wherein at least one
liquid rubber contains functional groups selected from the group
consisting of hydroxyl groups, carboxylic anhydride groups, and
combinations thereof.
32. The composition of claim 27 containing at least two liquid
rubbers, one liquid rubber having a high percentage of
Cis-1,4-double bonds and another liquid rubber having a high
percentage of vinyl double bonds.
33. The composition of claim 27, wherein from 1% to 5% by weight
calcium oxide is used as one of the fillers.
34. The composition of claim 27 further containing at least one
ingredient selected from the group consisting of rheology aids,
tackifiers, extender oils, primers, and mixtures thereof.
Description
This invention relates to one-component, hot-curing compositions
based on liquid rubbers and fine-particle powder-form thermoplastic
polymers and to their production and use as structural adhesives
with a breaking elongation of more than 15%.
BACKGROUND OF THE INVENTION
In modern assembly techniques for joining metal components in
machine construction, vehicle or equipment manufacture, more
especially in car manufacture, conventional methods of fixing, such
as riveting, screwing or welding, are being increasingly replaced
by bonding. Spot welding above all, which is a source of future
corrosion, is being displaced as far as possible or is being
applied in combination with structural adhesives. For this reason,
there is an increased demand for high-strength structural
adhesives. For assembly reasons, these adhesives have to be used at
the so-called white-shell stage of car manufacture, i.e. the
adhesives are generally applied to the uncleaned metal surface.
These surfaces are often coated with various corrosion-inhibiting
oils and drawing oils, so that the adhesives used there should not
be functionally affected by these oils. In addition, the adhesives
should be capable of withstanding--preferably without
pregelation--the various washing baths and installations and the
high temperatures of up to around 240.degree. C. prevailing in the
baking ovens for electrocoating and should also cure at
temperatures of that order. Moreover, the adhesives are required to
exhibit good ageing-resistant adhesion to various galvanized
steels, for example electrolytically galvanized steel plates,
hot-dip galvanized steel plates and the corresponding galvannealed
steel plates or galvanized and subsequently phosphated steel
plates. Structural adhesives for these applications must also have
a minimum strength of about 15 MPa. In the interests of smooth
assembly line operation, only one-component materials capable of
being transported by pumps and applied by machine are suitable.
On account of the demanding strength requirements, one-component
hot-curing epoxy adhesives have mainly been used for these
applications in the past. Apart from the advantages of high tensile
strength, however, epoxy adhesives have a number of major
disadvantages. The paste-like, hot-curing one-component epoxy
adhesives do not show adequate resistance to washing in the washing
and phosphating baths, so that the corresponding bonds normally
have to be pregelled by induction heating or in special ovens.
Unfortunately, this involves an additional step. Attempts have been
made to overcome this by developing one-component hot-curing epoxy
adhesives resembling hotmelts in character. Unfortunately, these
adhesives require special application systems because they have to
be applied hot. Another general disadvantage of epoxy adhesives is
their tendency to absorb moisture under the effect of high
atmospheric humidity which can lead to corrosion phenomena and
weakening of the bond in the bond line. Although epoxy adhesives
are distinguished by high tensile strength, their breaking
elongation is generally very poor; even epoxy adhesives
flexibilized by addition of rubber have a breaking elongation of
less than 5%. In addition, the use of epoxy adhesives based on low
molecular weight epoxy compounds (molecular weight<700) is
undesirable on industrial hygiene grounds because these low
molecular weight epoxy compounds can initiate allergic or
sensitizing reactions on contact with the skin.
For some time, compositions based on vulcanizable rubbers have been
used as an alternative. EP-B-97 394 describes an adhesive mixture
based on a liquid polybutadiene rubber, powder-form sulfur, organic
accelerators and optionally solid rubber. According to B. D.
Ludbrook, Int. J. Adhesion and Adhesives, Vol. 4, No. 4, pages
148-150, corresponding adhesives based on liquid polybutadienes are
capable of attaining strength levels equivalent to those of
flexibilized epoxy adhesives through an appropriate choice of the
quantity of sulfur and accelerators. Whereas these formulations
have good curing properties and show high resistance to ageing and
even adhere acceptably to normal oiled steel plate, their
usefulness for various galvanized steel plates is limited, in
addition to which the breaking elongation of these high-strength
rubber adhesives is very poor.
To improve adhesion, DE-C-38 34 818 proposes using OH-terminated
polybutadienes for the liquid rubber. According to EP-B-441 244,
homopolymers or copolymers containing thiol, amino, amido,
carboxyl, epoxy, isocyanate, anhydride or acetoxy groups may be
used in addition to hydroxyfunctional homopolymers or copolymers as
the functional rubber polymer, although the cured adhesive mixture
has a breaking elongation of no more than 15%.
According to EP-B-309 903 and DE-C-40 27 064, polyfunctional epoxy
compounds may be added to the adhesive mixtures based on liquid
rubbers to improved adhesion and tensile shear strength. Apart from
the fact that it is undesirable for the reasons explained above to
use adhesive compositions containing epoxy resin, the adhesive
compositions disclosed in the last two documents are not suitable
as structural adhesives because they only reach a very low strength
level of at most 3 MPa.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
Not applicable.
DETAILED DESCRIPTION OF THE INVENTION
Accordingly, the problem addressed by the present invention was to
provide adhesives and sealants which could be used with advantage
for joining metal parts in automobile shells ("white shells") and
which
would show adequate permanent adhesion on a number of the metal
surfaces used today without any need for cleaning
pretreatments,
could be used as structural adhesives (structural adhesives in the
context of the invention being adhesives which attain a strength of
at least 15 MPa in tensile shear tests),
would have a breaking elongation according to DIN 53504 of more
than 15% and preferably more than 20%, in addition to which
the materials would comprise one component, would be hot-curing and
would cure at temperatures of 160.degree. C. to 240.degree. C.,
their strength properties not being significantly affected by the
curing temperature.
Apart from normal oiled steel plates, substrates on which adhesion
must be obtained include, in particular, the various galvanized and
oiled steel plates and aluminium.
According to B. D. Ludbrook loc. cit., the strength values of
rubber-vulcanized adhesives can be significantly increased by the
quantity of sulfur and accelerator, but always to the detriment of
breaking elongation. It has surprisingly been found that the
addition of fine-particle powders of thermoplastic polymers to
adhesives based on liquid rubbers not only increases tensile shear
strength, it also significantly improves breaking elongation. Since
the other properties, for example ageing resistance and adhesive
behavior on the substrates mentioned above, are not affected by the
addition of the thermoplastic polymer powder, the adhesives in
question are very much more universal in their usefulness. Thus,
structural adhesives may even used for the first time where,
hitherto, it has only been possible to use adhesives with lower
strength levels on account of the high elasticity required, as is
the case for example with lining adhesives for bonding inner panels
to outer panels in car manufacture where high torsional rigidity is
required for structural reasons.
The adhesive/sealant compositions according to the invention
contain at least one of the following substances:
one or more liquid rubbers and/or solid rubbers or elastomers
fine-particle powders of thermoplastic polymers
vulcanization agents, vulcanization accelerators, catalysts
fillers
tackifiers and/or primers
extender oils
antiagers
flow aids.
Liquid rubbers or elastomers may be selected from the following
group of homopolymers and/or copolymers:
Polybutadienes, more particularly 1,4- and 1,2-polybutadienes,
polybutenes, polyisobutylenes, 1,4- and 3,4-polyisoprenes,
styrene/butadiene copolymers, butadiene/acrylonitrile copolymers;
these polymers may have terminal and/or (statistically distributed)
lateral functional groups. Examples of such functional groups are
hydroxy, amino, carboxyl, carboxylic anhydride or epoxy groups. The
molecular weight of these liquid rubbers is typically below 20,000
and preferably between 900 and 10,000. The percentage content of
liquid rubber in the composition as a whole depends upon the
required rheology of the uncured composition and the required
mechanical properties of the cured composition. The percentage
content of liquid rubber or elastomer normally varies between 5 and
50% by weight, based on the formulation as a whole. It has proved
to be useful in this regard to employ mixtures of liquid rubbers
differing both in their molecular weight and in their configuration
in relation to the remaining double bonds. To achieve optimal
adhesion on various substrates, a liquid rubber component
containing hydroxyl groups or anhydride groups is used in the
particularly preferred formulations. At least one of the liquid
rubbers should have a high percentage content of cis-1,4-double
bonds while another liquid rubber should have a high percentage of
vinyl double bonds.
By comparison with liquid rubbers, suitable solid rubbers have a
significantly higher molecular weight (MW=100,000 or higher).
Examples of suitable rubbers are polybutadiene, preferably with a
very high percentage of cis-1,4-double bonds (typically above 95%),
styrene/butadiene rubber, butadiene/acrylonitrile rubber, synthetic
or natural isoprene rubber, butyl rubber or polyurethane
rubber.
The addition of fine-particle thermoplastic polymer powders
produces a significant improvement in tensile shear strength while
maintaining a very high breaking elongation hitherto untypical of
structural adhesives. Thus, tensile shear strengths of more than 15
MPa can be achieved for breaking elongations well above 15% and,
very often, above 20%. The high-strength structural adhesives
hitherto typically used were based on epoxy resins which only have
breaking elongations of less than 5%, even as flexibilized adhesive
formulations. The combination of high tensile shear strength values
with high breaking elongation is attributed to the addition of
thermoplastic polymer powders in accordance with the invention.
According to the invention, numerous thermoplastic polymer powders
are suitable additives, including for example vinyl acetate either
in the form of a homopolymer or in the form of a copolymer with
ethylene and other olefins and acrylic acid derivatives, polyvinyl
chloride, vinyl chloride/vinyl acetate copolymers, styrene
copolymers of the type described, for example, in DE-A-40 34 725,
polymethyl methacrylate and copolymers thereof with other
(meth)acrylates and functional comonomers, for example of the type
described in DE-C-24 54 235, or polyvinyl acetals, for example
polyvinyl butyral. Although the particle size or rather particle
size distribution of the polymer powders does not appear to be
particularly critical, the average particle size should be below 1
mm, preferably below 350 .mu.m and, more preferably, between 100
and 20 .mu.m. Polyvinyl acetate and copolymers based on
ethylene/vinyl acetate (EVA) are most particularly preferred. The
quantity of thermoplastic polymer powder added is determined by the
required strength range and is between 2 and 20% by weight, based
on the composition as a whole, a particularly preferred range being
from 10 to 15%.
Since the crosslinking or curing reaction of the rubber composition
has a critical influence on the tensile shear strength and breaking
elongation of the cured adhesive composition, the vulcanization
system has to be selected and adapted with particular care. Various
vulcanization systems based on elemental sulfur and vulcanization
systems with no free sulfur may be used. Vulcanization systems with
no free sulfur include those based on thiuram disulfides, organic
peroxides, polyfunctional amines, quinones, p-benzoquinone dioxime,
p-nitrosobenzene and dinitrosobenzene and also systems crosslinked
with (blocked) diisocyanates. Vulcanization systems based on
elemental sulfur and organic vulcanization accelerators and also
zinc compounds are most particularly preferred. The powder-form
sulfur is used in quantities of 4 to 15% by weight, based on the
composition as a whole, quantities of 6 to 8% being particularly
preferred. Suitable organic accelerators are the dithiocarbamates
(in the form of their ammonium or metal salts), xanthogenates,
thiuram compounds (monosulfides and disulfides), thiazole
compounds, aldehyde/amine accelerators (for example
hexamethylenetetramine) and also guanidine accelerators,
dibenzothiazyl disulfide (MBTS) being most particularly preferred.
These organic accelerators are used in quantities of 2 to 8% by
weight, based on the formulation as a whole, and preferably in
quantities of 3 to 6%. In the case of zinc compounds acting as
accelerators, a choice may be made between the zinc salts of fatty
acids, zinc dithiocarbamates, basic zinc carbonates and, in
particular, fine-particle zinc oxide. The content of zinc compounds
is in the range from 1 to 10% by weight and preferably in the range
from 3 to 7% by weight. In addition, other typical rubber
vulcanization agents, for example fatty acids (for example stearic
acid), may be present in the formulation.
Although, in general, the compositions according to the invention
already show very good adhesion to the substrates to be bonded by
virtue of the presence of liquid rubber containing functional
groups, tackifiers and/or primers may be added where necessary.
Suitable tackifiers and/or primers are, for example, hydrocarbon
resins, phenolic resins, terpene/phenol resins, resorcinol resins
or derivatives thereof, modified or unmodified resinic acids or
esters (abietic acid derivatives), polyamines, polyaminoamides,
anhydrides and anhydride-containing copolymers. The addition of
polyepoxy resins in small quantities (<1% by weight) can also
improve adhesion to some substrates. In this case, however, solid
epoxy resins with a molecular weight well above 700 are preferably
used in finely ground form so that the formulations are still
substantially free from epoxy resins, more especially those with
molecular weights below 700. If tackifiers or primers are used, the
type and quantity used will depend upon the polymer composition of
the adhesive/sealant, upon the required strength of the cured
composition and upon the substrate to which the composition is
applied. Typical tackifying resin (tackifiers), for example
terpene/phenol resins or resinic acid derivatives, are normally
used in concentrations of 5 to 20% by weight while typical primers,
such as polyamines, polyaminoamides or resorcinol derivatives, are
used in concentrations of 0.1 to 10% by weight.
The compositions according to the invention are preferably free
from plasticizers for the thermoplastic polymer. More particularly,
they are free from phthalic acid esters. However, it may be
necessary to influence the rheology of the uncured composition
and/or the mechanical properties of the cured composition by
addition of so-called extender oils, i.e. aliphatic, aromatic or
naphthenic oils. However, this influence is preferably exerted
through the appropriate choice of the low molecular weight liquid
rubbers or through the use of low molecular weight polybutenes or
polyisobutylenes. If extender oils are used, they are used in
quantities of 2 to 15% by weight.
The fillers may be selected from a number of materials, including
in particular chalks, natural ground or precipitated calcium
carbonates, calcium/magnesium carbonates, silicates, heavy spar and
also carbon black. Lamellar fillers, for example vermiculite, mica,
talcum or similar layer silicates, are also suitable as fillers. It
may be useful for the fillers to be at least partly
surface-pretreated. Coating with stearic acid to reduce the
moisture introduced and to prevent the cured composition from
becoming sensitive to moisture have proved to be particularly
useful for the various calcium carbonates or chalks. In addition,
the compositions according to the invention generally contain
between 1 and 5% by weight of calcium oxide. The total content of
fillers in the formulation can vary from 10 to 70% by weight and is
preferably in the range from 25 to 60% by weight.
Conventional stabilizers, for example sterically hindered phenols
or amine derivatives, may be used to prevent thermal,
thermo-oxidative or ozone degradation of the compositions according
to the invention, these stabilizers typically being used in
quantities of 0.1 to 5% by weight.
Although the rheology of the compositions according to the
invention can normally be brought into the required range through
the choice of the fillers and the quantity ratio of the low
molecular weight liquid rubbers, conventional rheology aids, for
example pyrogenic silicas, Bentones or fibrillated or pulped
chopped strands may be added in quantities of 0.1 to 7%. In
addition, other conventional auxiliaries and additives may be used
in the compositions according to the invention.
As mentioned at the beginning, a preferred application for the
one-component hot-curing adhesive/sealant composition according to
the invention is in white-shell assembly in the car industry, so
that the compositions should cure in 10 to 35 minutes at
temperatures of 80 to 240.degree. C., temperatures of 160.degree.
C. to 200.degree. C. preferably being applied in white-shell
assembly. A major advantage of the compositions according to the
invention over known paste-form one-component epoxy resin adhesives
lies in their so-called "washing resistance" immediately after
application of the adhesives, i.e. they do not require pregelation
in the same way as the above-mentioned epoxy adhesives to be
resistant to the various washing and phosphating baths used in
white-shell assembly. The compositions according to the invention
have the advantage over hotmelt epoxy adhesives that they need only
be gently heated to around 30 to 45.degree. C. for pumping and for
application, in addition to which their wetting power for cold
substrates is considerably better than that of epoxy hotmelts by
virtue inter alia of their greater inherent tackiness.
EXAMPLES
The following Examples are intended to illustrate the invention
without limiting it in any way.
To determine tensile shear strength, 1.5 mm thick strips of a 14 O5
steel measuring 25.times.100 mm were bonded with the adhesives with
an overlap of 25.times.20 mm; the layer thickness of the adhesive
was 0.2 mm. The steel strips had been oiled beforehand with ASTM
Oil No. 1, coating weight 3 to 4 g/m.sup.2. Breaking elongation and
tear strength were determined on an S2 test specimen according to
DIN 53 504, layer thickness 2 mm. A conventional laboratory tensile
testing machine was used for both tensile tests (rate of advance 50
mm/min.). The adhesives were cured in a laboratory circulating-air
oven, cure time: 30 mins. at 180.degree. C.
In an evacuable laboratory kneader, the compositions identified in
the following Tables were mixed in vacuo until they were
homogeneous. Unless otherwise indicated, all parts in the Examples
are parts by weight.
TABLE 1 ______________________________________ Comparison
Comparison Example 1 Example 1 Example 2
______________________________________ Polybutadiene, solid (1) 5.0
5.0 5.0 Polybutadiene, liquid (2) 5.0 5.0 5.0 Polybutadiene, liquid
(3) 15.0 15.0 15.0 Polybutadiene, liquid (4) 5.0 5.0 5.0 Zinc
oxide, active 4.0 4.0 4.0 Sulfur, powder 7.0 5.0 7.0 Dibenzothiazyl
disulfide 5.0 5.0 5.0 (MBTS) Polyvinyl acetate, powder (5) 10.0 --
-- Calcium carbonate 41.0 53.0 51.0 Calcium oxide 2.5 2.5 2.5
Antioxidant 0.5 0.5 0.5 Tensile shear strength 18.3 MPa 8.2 MPa
14.7 MPa Breaking elongation 26.0% 57.3% 4.96% Tear strength 16.5
MPa 7.0 MPa 14.5 MPa ______________________________________ (1)
Cis1,4 at least 98%, Mooney viscosity 48 (ML4100) (2) MW about
1800, cis1,4 about 72% (3) MW about 1800, vinyl about 40-50% (4)
Polybutadiene/maleic anhydride adduct, MW about 1700 (5) EVA
copolymer, Tg about 23.degree. C.
TABLE 2 ______________________________________ Comparison Example 2
Example 3 Example 4 Example 1
______________________________________ Polybutadiene, 5.0 5.0 5.0
5.0 solid (1) Polybutadiene, 5.0 5.0 5.0 5.0 liquid (2)
Polybutadiene, 15.0 15.0 15.0 15.0 liquid (3) Polybutadiene, 5.0
5.0 5.0 5.0 liquid (4) Zinc oxide, active 4.0 4.0 4.0 4.0 Sulfur,
powder 5.0 5.0 5.0 5.0 Dibenzothiazyl 5.0 5.0 5.0 5.0 disulfide
(MBTS) Polyvinyl chloride (5) 10.0 -- -- -- Styrene -- 10.0 -- --
methacrylate (6) Polymethyl -- -- 10.0 -- methacrylate (7) Calcium
carbonate 43.0 43.0 43.0 53.0 Calcium oxide 2.5 2.5 2.5 2.5
Antioxidant 0.5 0.5 0.5 0.5 Tensile shear strength 9.4 MPa 9.8 MPa
11.9 MPa 8.2 MPa Breaking elongation 46.7% 34.1% 29.5% 57.3% Tear
strength 8.2 MPa 7.0 MPa 9.9 MPa 7.0 MPa
______________________________________ (1) Cis1,4 at least 98%,
Mooney viscosity 48 (ML4100) (2) MW about 1800, cis1,4 about 72%
(3) MW about 1800, vinyl about 40-50% (4) Polybutadiene/maleic
anhydride adduct, MW about 1700 (5) Emulsion PVC, K value 70 (6)
Styrene copolymer according to DEA-40 34 725, 7.5% methacrylic acid
(7) PMMA containing copolymerized vinyl imidazole
In the tensile shear strength test, cohesive failure was observed
with all test specimens.
The only plate thicknesses available for determining adhesion
behavior on galvanized steel were the plate thicknesses of 0.8 mm
typically used in the automotive industry. However, high-strength
structural adhesives of the present examples are already in the
strength range of these thin steel plates so that the adhesion
behavior on these substrates could only be evaluated by a
qualitative peel test. To this end, the steel plates were oiled
with ASTM Oil No. 1, coated with the adhesive, oven-cured as
described above and then evaluated in a manual peel test. The
following substrates were tested: electrolytically galvanized,
hot-dip galvanized, galvanized and phosphated and galvannealed
steel plates. Cohesive failure was observed in every case.
As can be seen from a comparison of Comparison Example 1 with
Comparison Example 2, the tensile shear strength or tear strength
of the rubber-based adhesives according to the prior art can be
significantly increased solely through a higher content of sulfur,
although at the same time there is a drastic reduction in breaking
elongation. The addition of polyvinyl acetate copolymer (Example 1)
in accordance with the invention produces a significant increase in
tensile shear strength but, at the same time, keeps breaking
elongation at a high level (26%). As can be seen by comparing
Comparison Example 1 (no addition of thermoplastic powder) with
Examples 2 to 4, tensile shear strength can be significantly
increased by this addition, despite a low sulfur content, through
the addition of the various thermoplastic powders with only a very
slight reduction in breaking elongation.
* * * * *